It is oftentimes necessary, or at least desirable, to copy data stored on a media such as magnetic tape. It is likewise often desirable and/or necessary to generate multiple copies such as, for example, where copies are to be widely distributed.
In conventional data copying, a conventional (or, in some cases, a specialized) computer is used to read data into memory. A ring buffer is normally utilized to receive and maintain the data until it is used, or written out, to output devices. Since speed can be considered to be a measure of efficiency in data copying, the faster the computer provides information to the output devices and accepts data from the input devices, the more efficient the copying device.
As conventional computers only access data from a single location at a time, as more output devices are attached (as would be necessary to accommodate the generation of more concurrent copies, for example), greater computer speed is required to satisfy the additional request for data to be written.
In order to maximize copying speed, specialized computers have heretofore been developed with exceptionally high input-output speed (i.e., having high I/O bandwidth) capable of acknowledging up to three million independent I/O requests per second.
However, as increasingly dense, higher throughput data storage devices became more common, substantially higher data speeds became necessary. In order to obtain sufficient cycle speeds necessary to keep up with these devices, as well as to maintain a high copy fanout (typically 1 to 8), necessary speeds have been found to exceed those obtainable with conventional, inexpensive computer memory devices now known.
At the same time, however, the cost of conventional computer memory devices has been reduced so that utilization of a plurality of memories has become practical.
Various copying devices have been heretofore suggested in prior art patents, including a system for copying of data from a master disk onto a plurality of slave disks synchronized with the master disk (see U.S. Pat. No. 4,618,897), a system for copying of data from one tape to a second tape utilizing an optical storage device (see U.S. Pat. No. 4,320,486), and various systems for generating a plurality of tapes having digital information copied thereon from a master tape (see U.S. Pat. Nos. 3,805,284, 4,375,655 and 4,410,917). In addition, at least one such known system has also include circuitry for verifying data transferred (see U.S. Pat. No. 3,805,284).
As can be appreciated from the foregoing, while various systems have been heretofore suggested for providing multiple copies of information including multiple copies of taped digital information, such systems have normally utilized a single memory unit that is commonly associated with multiple copy producing units. This, however, has resulted in relatively slow copy generation where each copy is sequentially made by sequential accessing of the common memory. While concurrent production of copies from a single memory could speed up copy generation, such production has not been found practical due, at least in some instances, to loss of integrity of data copied and/or due to complications arising in compensating for varying characteristics of the various tape drive units utilized.
A need, therefore, has still existed for a system capable of dependably producing multiple copies of taped data at a relatively high rate of speed.